How to move form UK to California?

I am living in uk at the moment and it is my dream to move to long beach. I m 18 at the moment and i want to move after i finish uni in 3 years after ive saved up a bit of money. I wanna go with a couple of friends so we can split the cost of a house and rent. Can someone explain to me how I move, what do i need, for example a visa and how do i get one? Do I need a greencard and if so how do i get one? Do I need to apply for a job before I move or go first and just hope I can get the job I want? I looked at houses and found one for $99,999. It said the mortgage could be paid monthly but only over 15 years or 30 years, but what if i dont wanna stay that long? Please help I feel so confused by all this.

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